Principal Noise Sources Research Articles

Dynamic sensitivity and thermal noise analysis of a magnetoelastic amorphous metal low-frequency magnetometer

The ferromagnetic susceptibility of a magnetoelastic amorphous metal ribbon is determined from the coupled equations of motion for the magnetization and strain modes. This analysis is used to calculate the dynamic sensitivity and field equivalent noise floor of a metallic glass low-frequency magnetometer. Two principal noise sources are considered: the thermally induced magnetization fluctuations and the Johnson noise of the pick-up coil. The magnetometer exhibits a calculated minimum detectable field of ∼0.1 pT/(Hz)1/2 for room temperature operation at a resonance frequency of 22 kHz and 103 turn pick-up coil having a 200-Ω resistance. The fundamental material limit is estimated to be ∼5 fT/(Hz)1/2.

Plumbing noise measurement and isolation

Plumbing noise measurements on valves used for domestic lavatories, showers, tubs, and toilets have been measured utilizing the approach outlined in ISO Standard 3822. This technique evaluates the flow induced structural vibration transmitted into the piping system. The results clearly indicate that the principal source of noise is turbulence within the valve mechanism and not due to excessive velocities in the piping. Comparisons will be provided between American and European products. Several standard methods of isolating pipe wall vibration from building components are also evaluated.

Radio frequency spectral characteristics of an HVDC converter station

The radio frequency (RF) energy levels in a DC converter switchyard and valve halls have been measured in order to gain insight into the RF performance of converter stations. Detailed extended spectral records were taken at selected points within the valve halls, and at selected points and traverses in the DC yard to establish the converter station characteristic or signature. The purpose of the study is the detection and absolute quantification of the electric and magnetic field strengths at the test locations. To obtain the maximum amount of information about a converter pole when it is considered as an RF source, swept frequency (broad band) noise measurements were selected as the prime records for the analysis of the performance. The principal source of the RF noise is clearly the igniting valve. Several observations were made based on the measurements related to the initial slope of the voltage collapse recorded within the valve hall, the role of the distant grounding electrode, and the ignition pulse that produces an ω −2 spectral decay. The information will prove useful for (a) identification of the phenomena or station components shaping the station signature, (b) potential RF filtering applications in transmission line carrier bands, (c) the comparison of field and model tests performed by similar but scaled instrumentation systems.

Reduction of discrete frequency noise in small, subsonic axial-flow fans

The discrete frequency noise radiated from representative tyes of axial-flow fans used in electronic equipment is studied in detail. Narow-band analysis of the discrete frequency noise radiated by these types of fans has been conducted in an anechoic environment. The farfield sound pressure level and radiated directivity of the discrete frequency noise are presented. The influence of operating condition on the radiated sound is determined. The discrete frequency noise dominates the characteristic acoustic spectra at high flow coefficients. The radiated directivity of the discrete frequency noise is generally uniform. Based on the data collected and on the theoretical aspects presented, the principal source of the discrete frequency noise is identified for each of the fans as the interaction of the fan rotor with a circumferentially distorted, nonuniform flow. A collection of prototype design modifications is developed for each representative fan to reduce the radiated discrete frequency noise by improving the uniformity of the local flow field. A modified prototype configuration is developed for each representative fan which is evaluated acoustically and compared to the original baseline data.

Is stellar differential rotation observable?

Daily measures of the disk integral 2.8 GHz solar flux from the years 1947 through 1982 are analyzed to determine the detectability of stellar differential rotation using the tracer method. Autocorrelation and power spectral analyses of 1 yr data sets yield rotation periods whose scatter about the mean period is too large to permit detection of the expected differential rotation signal. The principal noise source is the random appearance of tracer regions on the solar surface, in time and longitude. Criteria are given for optimizing stellar observations and analyses to detect differential rotation.

Relationship between dielectric properties of SBN and their effect on pyroelectric detection

Measurements of permittivity and tan δ in poled SBN are obtained as functions of frequency. Their effects on pyroelectric detection are calculated and analyzed. For the frequency range in which the thermal noise caused by the dielectric losses of the material is the principal noise source, the variation of tan δ with frequency has an obvious effect on the pyroelectric detection.

Heterojunction phototransistors for long-wavelength optical receivers

We demonstrate by measurement and analysis that previously reported InP/InGaAs heterojunction phototransistors are promising photodetectors for long-wavelength optical receivers. The gain characteristics of these devices are shown to reflect the benefit of a wide band-gap emitter as well as the effects of recombination centers near the base-emitter heterojunction. In order to analyze the noise characteristics we derive a model which accounts for the three principal noise sources: the shot noise of the base current, the shot noise of the collector current, and the thermal noise of the load resistor. Using this model and experimental device parameters, we calculate the sensitivity of an optical receiver which utilizes a heterojunction phototransistor. This calculation indicates that the performance of this monolithic device can be as good as or exceed that of a hybrid p–i–n photodiode/field effect transistor-preamplifier combination.

Noise from opencast coal mining sites

The principal sources of noise in opencast coal mining operations are described. Currently available information on the assessment, prediction, measurement and control of this type of noise is considered. Some of the problems associated with the setting up of a scheme for the control of noise from opencast sites which are discussed are found to apply to other sources of environmental noise. It is concluded that at present there is insufficient information available to enable a scheme covering all aspects of noise control to be produced. Suggestions are made for further research.

Land Gas Turbine Exhaust Noise

An acoustic test program on a 1/7-scale model of the exhaust configuration for a General Electric MS 5000 gas turbine has been carried out. The tests were designed to isolate the noise contributions of the individual exhaust system components and to identify the additional noise due to combinations of two or more components. This model of the MS 5000 system was found to have three principal noise sources. At a high degree of turbine exit swirl all three sources appear with the most dominant due to an interaction between aft bearing support strut wakes and downstream exhaust hood turning vanes. At zero swirl the isolated turning vane noise and an exhaust hood plenum resonance are the remaining principal noise sources. A rather unexpected effect was uncovered in the course of this program; a strong reduction in the noise generation of separated flow downstream of struts and vanes was observed when a diffuser was placed immediately behind the strut or vane exit plane. This reduction in noise was much greater than could be attributed to the reduction in velocity caused by the diffuser.

Programming noise control in a small caliber munitions manufacturing plant

Program costs for the implementation of plant-wide noise control through retrofit of existing equipment were developed for a high-volume munitions manufacturing facility. Noise reduction costs were estimated by defining workable approaches for the control of all noise sources. Involved were over 1200 machines and some 37 different manufacturing operations. The principal noise sources were punch presses, parts hoppers, parts feed chutes, conveyor lines, tumblers, and other automatic metal-forming and transfer machines. The most prevalent generating mechanisms were the part impacts during transfer and part impact and surface vibration at the punch presses. The goal was to reduce the existing conditions, reaching 110 dBA in certain locations, to below the U. S. Army's 85 dBA non-time-weighted hearing conservation criterion. The level of design detail of the noise control developed was limited to that required for cost estimation. Design detail for fabrication was not provided since the principal objective was to provide management with program cost data. This crucial information can now be factored into the capital equipment planning function along with traditional projections such as economic equipment life, future production requirements, and equipment modernization schedules.

The silencing of a high performance motorcycle

The noise output of a 750 cc motorcycle was reduced from, 98 dB(A) to 86 dB(A) under current European test conditions, without significant power loss. Principal noise sources were exhaust, induction, and mechanical noise, with induction noise being higher than expected, and the untreated mechanical noise mainly responsible for the final level settling no lower than 86 dB(A). Induction noise was reduced by 12 dB(A) by using a damped cavity side-resonator, and exhaust noise by 20 dB(A) (compared with standard silencer equipment) by using a new silencing principle. Both intake and exhaust silencers were inexpensive to produce, of compact dimensions, and presented no special manufacturing problems.

Apartment noise, auditory discrimination, and reading ability in children

This study examined the relationship between a child's auditory and verbal skills and the noisiness of his home. Expressway traffic was the principal source of noise. Initial decibel measurements in a high-rise housing development permitted use of floor level as an index of noise intensity in the apartments. Children living on the lower floors of 32-story buildings showed greater impairment of auditory discrimination and reading achievement than children living in higher-floor apartments. Auditory discrimination appeared to mediate an association between noise and aeading deficits, and length of residence in the building affected the magnitude of the correlation between noise and auditory discrimination. Additional analyses ruled out explanations of the auditory discrimination effects in terms of social class variables and physiological damage. Partialling out social class did, however, somewhat reduce the magnitude of the relationship between noise and reading deficits. Results were interpreted as documenting the existence of long-term behavioral aftereffects in spite of noise adaptation. Demonstration of postnoise consequences in a real-life setting supplement laboratory research showing the stressful impact of noise on behavior.

Near-Field Environments of VTOL Jets

For jet-powered VTOL aircraft, the principal sources of nearfield noise are the direct and ground-reflected noise of the jet exhaust, the aerodynamic noise from wall jet formed by the deflected exhaust flow and the noise of the impinging jet. These principal sources are considered and several of their basic characteristics for VTOL jet noise are established. Emphasis is placed on the change in acoustic power and near-field levels due to their combined effect. A prediction method for near-field noise of VTOL jets is then outlined in the form of additive corrections to apply to near-field levels for the undeflected jet. These corrections have a maximum value of about 15–20 dB in the range of typical resonance frequencies for flight vehicle skin panels. However, these additive corrections vary substantially with frequency and elevation of the vertically directed nozzle. The approximate trend in these variations is illustrated based on the results of model studies. [This work was supported by the Air Force Flight Dynamics Laboratory, Wright-Patterson Air Force Base, Ohio.]

Systems Analysis of a TDM-FDM Translator/Digital A-Type Channel Bank

In keeping with the trend to greater use of digital circuits for signal processing, a project was undertaken to realize in an exploratory way an important telecommunication function using as great a proportion of digital hardware as possible. The function chosen is that of the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</tex> -channel bank; viz., the frequency division multiplexing (FDM) of 12 voiceband signals onto a single wire. Because of the nature of its operation the device to be described can also perform a translation between FDM analog signals and time division multiplexed (TDM) digital signals. This paper describes the overall system design of the device with particular emphasis on a noise analysis. The principal sources of noise are the A/D conversion points and the roundoff points that occur at the outputs of multipliers. Each noise source is examined in turn and its contribution to the total noise assessed. It is concluded that the A/D conversion points are the most important noise sources and the most costly to deal with.

On the noise sources of the unsuppressed high-speed jet

The paper describes an interpretation of jet-noise theory and scale-model experiments to highlight physical properties of jet-noise sources at very high speed. The study is prompted by current efforts to suppress the noise of supersonic transport aircraft.The principal noise sources are shown to be very large-scale wave-like undulations of the jet flow that travel downstream at supersonic speed for a distance of several jet diameters. These motions are relatively well ordered and are probably more akin to recognizable instabilities of a laminar flow than the confused small-scale turbulence. Because of this we postulate a model of the noise generating motions as the instability products of a jet flow of low equivalent Reynolds number. This Reynolds number is based on an eddy viscosity and can be further reduced by artificially increasing the small-scale turbulence level. This step would tend to stabilize the flow and inhibit the formation of large-scale noise producing eddies.

A Double-Electrode Method of Spontaneous Potential Logging

Koerperich, E.A., SPE-AIME, Shell Oil Co. In this method of logging, a recording of the potential difference between two SP electrodes yields a curve that may facilitate and improve sand counts, and that might be amenable to automatic computerized interpretation. Spurious SP electrode noise signals can be substantially reduced or eliminated from the potential-difference curve. Introduction Wellbore SP currents and their applicability in the location of subsurface sand bodies were discovered in 1931 and the usefulness of this measurement has persisted to the present day. Through the steadfast persisted to the present day. Through the steadfast endeavors of many researchers, knowledge and understanding of the SP has slowly evolved from the original mere recognition of its existence to its present-day quantitative use. Some common applications present-day quantitative use. Some common applications of the SP curve include bed correlation, sand counting and formation-water resistivity determination. This report relates to the determination of net sand counts from SP data. Many influences combine to complicate SP interpretation and to restrain its use as a unique, infallible indicator of permeable bed boundaries. The distribution and intensity of SP, currents are largely influenced by properties of the drilling and formation fluids. wellbore diameter and invasion depth, and by various characteristics of the subsurface strata. Quantitative use of the SP curve is severely restricted in salt, carbonate, and fresh water provinces, Shaly sand formations create difficulties with SP interpretation, and this topic has been the subject of many publications. An even greater problem is SP noise, which has long been a source of low-quality and erroneous SP curves, particularly since the advent of offshore drilling operations. A principal source of noise is associated with the surface "ground" potential to which the wellbore spontaneous potentials are referenced. Being located at the surface, the reference potential is vulnerable to voltage disturbances created by surface objects. Thus, all these factors that mold SP character should be accounted for, as adequately outlined in the literature, when the curve is being analyzed quantitatively. Many times the exact influence of some or all of these factors affecting SP response cannot be predicted. For this reason, auxiliary tools, whenever predicted. For this reason, auxiliary tools, whenever available, are used in conjunction with the SP to determine net sand. Short spaced, highly focused resistivity devices or pad-type resistivity devices are commonly used for this purpose. Despite the limitations of the SP curve, there are a number of occasions and areas where it satisfactorily reflects permeable bed boundaries. Many times auxiliary logs are not available to refine the SP sand count, leaving the SP as the primary indicator of bed boundaries. In these cases, the method of recording and presenting SP data as outlined in this report can presenting SP data as outlined in this report can usefully supplement the SP curve. This method of presentation is directly derived from a single conventional presentation is directly derived from a single conventional SP curve or from two conventional SP curves recorded simultaneously at different depths in the wellbore. When the data presentation is derived from a single down-hole electrode the resultant curve (Delta V curve) is subject to all the limitations and required corrections associated with the SP recording, including the presence of noise signals when they exist on the SP. When the, Delta V curve is derived from two downhole electrodes, it is subject to the same limitations except the SP noise. JPT p. 1437

Paper 8: The Diesel Engine as a Source of Commercial Vehicle Noise

The drive-past noise of diesel-engined commercial vehicles is controlled by engine speed rather than road speed. The principal noise source related to the power unit is the noise radiated by the engine structure, which has a level of 85–91 dBA during the ISO test. The combined intensity of all the other such sources is, at the most, equal to the noise radiated by the structure. It has been found that the parameters controlling engine noise are the bore, speed, and combustion systems. This has led to an empirical formula which predicts engine noise to within ±2 dBA.

Magnetostrictive offset and noise in flux gate magnetometers

Longitudinal magnetostriction of the core material is found to be the principal source of offset and noise in present state-of-the-art flux gate magnetometers. Magnetostrictive offset is identified with even harmonics of the steady-state induced EMF resulting from the periodic elongation (or contraction) of the core material. Magnetostrictive noise is identified with random fluctuations of the magnetostrictive offset caused by frictional forces exceeding the magnetostrictive stress when the core material is near zero elongation. An analytical model and experimental results of magnetostrictive offset and noise are presented. It is expected that flux gate magnetometers with zero magnetostriction of the core material will yield a significant increase in signal-to-noise ratio with corresponding decreases in offset and magnetomotive drive power.

Methods for Improving the Signal-to-Noise Ratio of Photon- and Electron-Beam-Accessed Magnetic-Film Memory Systems

Methods are described for reducing shot-noise in magnetic-film memories which are to be read magneto-optically with the auxiliary aid of an electron beam. In such memories the principal source of shot noise is from the light which is used to illuminate the memory array. The following methods of reducing array shot noise are considered: (1) selective background, (2) magneto-optical balance, (3) temperature control of magneto-optical spectra in rare-earth iron garnets (REIG). It is concluded that the use of REIG spectra appears to offer not only the best, but also a satisfactory solution to the array shot-noise problem.

Methods for improving the signal-to-noise ratio of photon and electron beam accessed magnetic-film memory systems

Methods are described for reducing shot noise in magnetic-film memories which are to be read magnetooptically with the auxiliary aid of an electron beam. In such memories the principal source of shot noise is from the light which is used to illuminate the memory array. The following methods of reducing array shot noise are considered: 1) selective background, 2) magnetooptical balance, 3) temperature control of magnetooptical spectra in rare-earth iron garnets (REIG). It is concluded that the use of REIG spectra appears to offer not only the best but also a satisfactory solution to the array shot-noise problem.